Since an LCD panel backlight apparatus uses a high-frequency AC sine wave power supply to provide energy for a cold cathode fluorescent lamp (CCFL) to emit lights, therefore a DC-to-AC circuit is used for the purpose of achieving the energy conversion. A traditional DC/AC inverter usually adopts one pulse width modulation controller (PWM controller) specifically designed for the DC/AC inverter to control the whole inverter circuit to supply a sufficient light source for all cold cathode fluorescent lamps to emit lights. However, a piece of PWM controller only has a voltage feedback input terminal, a current feedback input terminal and an abnormal status protection control input terminal, and the LCD panel backlight apparatus must be able to integrate each voltage input signal and each current input signal of the cold cathode fluorescent lamp and output a single voltage feedback signal and a current feedback signal to an input terminal of the PWM controller. On the other hand, the LCD panel backlight apparatus must be able to detect whether or not any cold cathode fluorescent lamp (CCFL) is short circuited (or touched by a human body) or open circuited (or not lit), so as to output an abnormal status protection signal to the PWM controller and turn off all outputs of the backlight apparatus to protect the inverter circuit and prevent damages to circuit components or injuries to people due to electric shocks. The present traditional way is to recreate a feedback and protection circuit by various different components, and thus many complicated components are required. Referring to FIG. 1 for a circuit block diagram of a traditional LCD panel backlight apparatus feedback and protection circuit, each pin of an input terminal CNl1 is connected to an input voltage, a reference ground, an enable signal and a dimming signal, wherein the switching switch control circuit 1 comprises a plurality of power transistors (not shown in the figure) and a PWM controller 2, and an output terminal of the PWM controller 2 outputs a plurality of control pulse waves for driving various different switch topologies to electrically conduct the power transistors (not shown in the figure), such that the input voltage terminal can be converted from a primary coil of the transformers T1˜T4 to a secondary coil to transmit energy. The leakage inductance of the secondary coil has a resonance with each serially connected capacitor to produce a sine wave voltage, which is outputted to two lateral sides of each cold cathode fluorescent lamp, such that the lamp emits lights to provide a light source of the backlight apparatus. The leakage inductance of a secondary coil of the transformer T 1 produces a resonance with capacitors C11, C12 connected in series; the leakage inductance of a secondary coil of the transformer T2 produces a resonance with capacitors C21, C22 connected in series; the leakage inductance of a secondary coil of the transformer T3 produces a resonance with capacitors C31, C32 connected in series; and the leakage inductance of a secondary coil of the transformer T4 produces a resonance with capacitors C41, C42 connected in series. Both terminals of output terminals CN1˜CN4 are connected to a cold cathode fluorescent lamp for receiving a resonance to produce AC sine wave power respectively. The purpose of capacitors C12, C22, C32, C42 is to output and divide each high voltage and pass the voltage to the diodes D11, D21, D31, D41 to obtain a maximum voltage value, and the voltage-divided resistors R3, R2 are inputted by a voltage feedback input terminal of the PWM controller 2. The purpose of the diodes D12, D22, D32, D42 is to clamp a negative voltage of the capacitors C12, C22, C32, C42 to the diodes and reduce the voltage to approximately −0.7V. After the diodes D15, D25, D35, D45 obtain the voltage at the terminals of the capacitors C12, C22, C32, C42, the voltage is divided respectively by resistors R14 and R15, R24 and R25, R34 and R35, and R44 and R45 and filtered by capacitor C13, C23, C33, C43 to conduct transistors Q11, Q21, Q31, Q41 in the situation of obtaining a sufficient normal operation time. If any lamp is short circuited, then the transistors Q11, Q21, Q31, Q41 cannot be electrically conducted with the reference ground, and the power voltage VCC will be charged immediately to a capacitor C3 through a resistor R5. If the capacitor C3 is charged to an operating voltage of the transistor Q1, the transistor Q1 will be conducted to pull a current feedback input terminal of the PWM controller 2 to a low potential, such that the PWM controller 2 stops outputting, and thus closing all outputs of the backlight apparatus, and the resistor R33 is used for discharging the energy of the capacitor C3.
Further, the resistors R11, R21, R31, R41 are connected between the cold cathode fluorescent lamp and the reference ground for obtaining a current detection signal. Diodes D14, D24, D34, D44 are used for clamping the negative voltage of the resistors R11, R21, R31, R41 to the diodes and reducing the voltage to approximately −0.7V. After the diodes D13, D23, D33, D43 obtain a maximum voltage value of the resistors R11, R21, R31, R41, the voltage is divided by resistors R4, R1 and inputted to a current feedback input terminal of the PWM controller 2. After diodes D16, D26, D36, D46 obtain voltages at the terminals of the resistors R11, R21, R31, R41, and the voltage is divided by the resistors R12 and R13, R22 and R23, R32 and R33, and R42 and R43 and filtered by the capacitors C14, C24, C34, C44, a sufficient normal operation time can be obtain to conduct the transistors Q12, Q22, Q32, Q42. If any lamp is open circuited, then the transistors Q12, Q22, Q32, Q42 cannot be conducted to the reference ground, and the power voltage VCC will immediately charge the capacitor C3 through the resistors R6. If the capacitor C3 is charged to an operating voltage of the transistor Q1, the transistor Q1 will be conducted to pull the current feedback input terminal of the PWM controller 2 to a low potential, so as to stop the output of the PWM controller 2, and close all outputs of the backlight apparatus. The shortcomings of the traditional circuit include a use of many distributed components to achieve the feedback and protection control circuit, and an increase of the level of difficulty and the area of the layout of the printed circuit board as well as an increase of cost of the overall inverter circuit, and a control of an excessively large range of operating voltages of the transistor, and thus modulations cannot be made properly or protections cannot be achieved.
Therefore, it is a subject for the present invention to create a feedback and protection circuit of a liquid crystal display panel backlight apparatus that simplifies a traditional feedback and protection circuit composed of various different components and achieve the effects of reducing the area occupied by the circuit component layout and lowering the overall cost.